> I would guess its a combination of "nobody sees the first hit".
No, it is done that way by purposeful intent, though you wouldn't recognize it as such without having studied and having a certain level of exposure to how torture works in reality (really dark stuff).
Bullying is a combination of physical and mental coercion. During Mao, the Chinese government discovered a number of ways to torture people to the point where they adopt false ideologies (effectively breaking them) for thought reform purposes.
These techniques are often embedded today in the structures used by teachers and they have predictable results. If the exposure is ongoing, people break, either through disassociation (helplessness/suicide), or psychosis seeking annihilation externally (albeit a semi-lucid psychosis capable of planning).
This is torture for thought reform, and Active shooters seem to fall into the latter bucket quite prominently. Unfortunately, Technology has made the ephemeral steps needed to do this (previously physically), possible (remotely).
Joost Meerloo, and Robert Lifton wrote about these structures and observations professionally covering the developments of the subject matter from WW2 through the Korean Conflict (1944-1960). They are well established experts.
Academia has a long problematic history of supporting things related to marxism. The most common telltale sign is that of circular structures (hegelian dialectic, or the abuse of the contrast principle). These are used to create convincing lies/deceits, critical theory (cultural-marxism/ i.e. the woke), originated from Marxists/Communists/Socialists (whose structure is almost objectively identical).
There are people in these systems who in action promote communism, while claiming otherwise. Whether they are lying, or are just delusional its hard to say but as I mentioned the telltale sign is circular structures. The first thing you need for rationalism is a common shared definition (what is called identity in philosophy). Then you can hold accountability following a system of logic. Without it, there is no accountability, and you can just as easily claim the exact opposite of the situation (Falsely), with no way to prove otherwise.
If you want an introduction to this not mired in a quagmire of deceit, I'd suggest Mises on Socialism (circa 1930s), it provides a rational introduction to the objective structure of such, without needing a lot of discernment to combat deceitful circular narratives inevitably found in other material.
Getting back to bullying, and torture, the gist is, all that is needed to coerce is components of isolation, lack of agency (on the part of the subject), and increasing cognitive dissonance. Its only then a matter of time and exposure, and certain structures allow meeting this criteria simultaneously for multiple different groups at once.
One such structure is called the hot potato, where a student is called out in front of class to answer a question. Usually fact questions are mixed in with thought reform opinions, and the student is not informed to mount a reliable defense. The subject when called is anxious or nervous, disapproval of their peers may result in bullying, lack of opportunity, or social stigma. This is determined and reflected by the approval or disapproval of the teacher in answering the question or correcting the question. Any disagreement is a reflection of disapproval. The more disagreement, the more disapproval.
There are always those seeking approval in the peer group, where disapproval results in those members bullying and harassment, or shunning, to seek approval, albeit arbitrarily with no explicit direction. This almost always happens outside class.
This structure induces both subject and peer group to participate in the dynamics, and in truth both are victims, since the harassment/needs of the peer group require them to act in ways that are consistent with the teachers approval (consistency principle). It doesn't matter if the teacher condemns such behavior verbally.
The idea of a struggle session (Maoist), is that you make life intolerable arbitrarily until you meet some unstated arbitrary measure. The subject is gaslit to believe its their fault, if only you would confess or agree (which invokes consistency). Sometimes there is no measure and its unending.
The route of effect is the same way we develop our identity and culture through communication within a community. Reflected Appraisal. As you are isolated, those you see most you begin to trust, they inadvertently affect you more until full conformity and adoption.
You generally must be in a vulnerable state either naturally (developmentally), or induced (through torture), to adopt behaviors in this way. The latter is effectively involuntary hypnotic suggestion which is induced.
These structures distort reflected appraisal, and use other sophisticated psychological biases to indoctrinate for purpose (avoiding critical thought/perception).
Unless you know what to look for, you don't even notice it being used against you to manipulate you. It is not of the flesh but over flesh. The seen and unseen. Tolkien often took inspiration from the bible, and Amazon's Rings of power are masterfully done in the way it depicts this subject matter.
If you've ever seen the movie Focus, what is described with choosing the player and number for the gambling con is truthful, and you can do far more than just that narrow example. Much of the foundational subject matter for these things was originally taught in a classical education (pre-prussian model of education), under Rhetoric. Science has allowed us to further probe what was known back then, effectively breaking perception, which reminds me of the Tower of Babel story.
If you would like a crash course in the blind spots, Robert Cialdini wrote a book, though he refers to them as levers of influence, unfortunately he doesn't touch on reflected appraisal in depth. The book is called Influence. Its been recognized in the US by members of the state department.
Many of these structural elements have been repackaged so as to obscure the fact that these originated from torture.
The Octalysis framework for game development for example hits most of these indirectly (albeit perfectly), but this is not an isolated example. Variations of the same structures are everywhere from business process, to CSR doom loops, basically anywhere you want to impose cost to coerce people against a specific behavior; these are used.
These situations and outcomes are by design, they are subtle and malign evil people often pretend, or rather believe that they are good. Know an evil person by the willful blindness they show to the consequences of their action, know an evil act by the destructive outcome that follows.
Know sloth by its more modern name, complacency (also the banality of evil), which turns towards radical evil.
If you would understand how these things happen, a thorough study of corruption, systems (and failures of such), history, and ruin are needed. Few get this education with modern curricula. Classical Curricula follow the greeks, (Trivium/Quadrivium). The rise and fall of the Roman Republic to Imperial Rome is also quite illustrative, and Social Contract Theory is a must (to understand what changes have caused civilized society to fail). The latter include Locke, Kant, Rosseau, Thomas Paine, and a few others.